JP-2009-516134A (WO-2007-059100A1) shows a valve apparatus which drives a valve in such a manner that a rotational movement of an output shaft of an electric actuator is converted into an axial movement of a slide shaft. In this valve apparatus, a link mechanism is employed to convert the rotational movement into the axial movement. A cam groove is formed on a cam plate rotating with a rotation shaft. When the cam plate and the cam groove are rotated, a cam follower engaging with the cam groove is driven, whereby a slide shaft is moved in its axial direction.
The rotation shaft is biased in a valve-close direction by a biasing force of a return spring. When the electric actuator becomes faulty, the valve is closed by the biasing force of the return spring. When the valve is opened, that is, when the valve body does not sit on a valve seat, the cam follower and slide shaft may vibrate due to an axial clearance gap between the cam groove and the cam follower.
It is conceivable that the return spring biases the slide shaft in a valve-close direction so that the cam follower and the slide shaft do not vibrate by the biasing force of the return spring even though the valve is opened. (This configuration is not prior art)
When the slide shaft is biased by the return spring in a valve-close direction and the valve body fully sits on the valve seat, the valve seat receives the biasing force of the return spring. Thus, when the valve is fully closed, the biasing force of the return spring is not transmitted to the rotation shaft.
The above operation will be specifically described, hereinafter.
A rotation angle range of the rotation shaft includes a backlash range (refer to “α” in FIG. 3) from a rotation-stop angle to a full-close angle. At the rotation-stop angle, the rotation shaft mechanically stops a rotation in valve-close direction (refer to θ0 in FIG. 3). The full-close angle is an angle of immediately before the valve starts opening (refer to θa in FIG. 3).
The rotation-stop angle and the full-close angle are not coincided with each other. In the backlash range, since the valve seat receives the biasing force of the return spring through the valve body, the rotation shaft does not receive the biasing force of the return spring.
In a case that a learning processing is performed with respect to the full-close angle and an output of a rotational angle sensor detecting the rotation angle of the rotation shaft, a first operation or a second operation is performed. In the first operation, the electric motor is energized in the valve-close direction and the rotation shaft is rotated until its rotation is stopped. In the second operation, the electric motor is deenergized and the valve is fully closed by the biasing force of the return spring only.
However, in a case of the first operation, the angle of the angle of the rotation shaft corresponds to the rotation-stop angle. Since the rotation-stop angle is different from the full-close angle, the learning processing can not be performed, in which the full-close angle and the output of a rotational angle sensor are made to correspond.
In a case of the second operation, the angle of the rotation shaft corresponds to an angle in the backlash range (refer to θx in FIG. 3). Since this angle in the backlash range is different from the full-close angle, the above learning processing can not be performed.